Groundwater and surface water influences on streamflow in a mesoscale Precambrian Shield catchment

Abstract

AbstractHydrologic research has increasingly recognized the importance of mesoscale studies to provide a fundamental understanding of how processes combine at scales relevant to water resource management. At the mesoscale, the influence of landscape heterogeneity including both natural and human‐altered conditions on streamflow generation is an open question, one to which analysis of stable water isotopes (SWI) is increasingly being applied. In this study, SWI surveys are used to better understand spatial and temporal patterns of source‐water contributions to streamflow in the Wistiwasing watershed (235 km2) located near Callander Bay, Ontario, Canada, a Precambrian Shield headwater with mixed landuse (e.g. agriculture, forest). Biweekly surveys of surface water, groundwater and precipitation were conducted during May to September 2012, and samples were analysed for SWI (δ18O and δ2H) using a Picarro L2120‐i. Maps of point‐scale surface water SWI were generated for each of the nine surveys, and an SWI isoscape, an interpolated contour map, was generated from groundwater observations. Based on a comparison of surface and groundwater SWI maps, regions of strong groundwater influence on streamflow were particularly identifiable during low‐flow, late‐summer conditions and corresponded with coarse‐textured glaciolacustrine deposits. Higher‐flow, early‐period conditions featured small SWI variation with values resembling long‐term groundwater recharge, a mix of snowmelt and spring/fall rains. Late‐period, low‐flow conditions indicated large spatial variability due to changing influences of groundwater and upstream surface water undergoing summertime evaporative enrichment of heavier isotopes. In this case study, SWI observations provide important insight into source‐water dynamics across a mesoscale watershed. Copyright © 2015 John Wiley & Sons, Ltd.